The goal of the proposed study is to determine the pattern generating capability and to characterize the segmental peripheral modulation of the spinal locomotor network subserving turtle swimming. The activity in twelve muscles or muscle-nerves will be employed to develop a high-resolution assay of the efferent output to a single hindlimb during controlled locomotion elicited via electrical stimulation of the dorsolateral funiculus of the spinal cord. The ability of the hindlimb enlargement of the spinal cord to generate a detailed locomotor pattern will be tested by comparing the efferent output obtained from the intact animal with the pattern acquired after sequential reduction of supraspinal and segmental afferent inputs. A standardized set of sensory inputs will be used to test the contributions of segmental afferent input to the patterning of the locomotor output during controlled locomotion of turtles which are deprived of supraspinal and movement-related afferent inputs. The regimen includes tonic, transient, and cyclical presentations of passive limb displacements, electrically elicited cutaneous afferent input, and electrically elicited proprioceptive input. The systematic re-introduction of sensory inputs, coupled with a detailed assessment of efferent output, will permit delineation of the variety of roles in which segmental afferent input aids in producing an efficacious locomotor output. The clinical importance of the proposed study lies in an expansion of our understanding of the roles of the central nervous system versus afferent feedback in the control of locomotion. In particular, clinical assessment and rehabilitation of CNS injured patients might benefit from more specific information regarding peripheral inputs which signal positional or stability conditions, or change rhythmic output frequency during locomotion.